ST AN2048 Application note

AN2048

Application note

PD54008L-E: 8 W - 7 V LDMOS in PowerFLAT packages for wireless meter reading applications

Introduction

STMicroelectronics has been strongly involved in finding new package solutions for power integrated circuits to obtain a surface mount device (SMD). The PowerFLAT™ package introduced in this application note shows the new concept of chip-size packaging representing a fundamental step to reduce the costs of assembly and to shrink power amplifier modules. This package helps maximize board space with improved electrical and thermal performances over traditional packages with leads. This leadless package is an MLP (micro leadframe package) where the electrical connections are made through landing pads on the bottom surface of the component. These landing pads are soldered directly to the pc board.

Figure 1. MLP cross section	Figure 2. Intermodulation distortion versus
	peak effective output power

The standard MLP has an exposed die attach pad which enhances the thermal and electrical characteristics enabling high-power and high-frequency applications. For small and medium-power applications, such as wireless PMR (private mobile radio) LDMOS (Laterally Diffused MOS) transistors in PowerFLAT packages offer certain advantages compared to equivalent bipolar transistors, for example, better intermodulation (IMD3). Under certain conditions, an LDMOS transistor exhibits better intermodulation distortion than a bipolar junction transistor. Figure 2 shows intermodulation distortion versus peak effective output power for equivalently rated bipolar and LDMOS transistors. As we can see, below 30 W, the LDMOS device has lower intermodulation distortion than the bipolar transistor.

●Good gain linearity

●Smooth saturation

●Simpler bias circuit

●Thermal stability. The drain current has a positive temperature coefficient, therefore the MOS transistor is not susceptible to thermal runaway.

●Better ruggedness

February 2008

Rev 2

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Contents	AN2048

Contents

1	Basic wireless meter reading system description . . . . . . . . . . . . . . . .		. 4
2	Electrical requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		4
3	Circuit design and considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		5
	3.1	Amplifier construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	5
4	Circuit schematic and bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . .		6
5	Transmission line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		7
	5.1	Characterization results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	7
6	Components layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		11
7	Characterization results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		12
8	Feature characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		12
9	References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		12
10	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		12

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AN2048	List of figures

List of figures

Figure 1. MLP cross section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Figure 2. Intermodulation distortion versus peak effective output power. . . . . . . . . . . . . . . . . . . . . . . 1 Figure 3. Network system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Figure 4. Source and load impedances of PD54008L-E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Figure 5. Device footprint. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Figure 6. Cross section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Figure 7. Broadband power amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Figure 8. Transmission line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Figure 9. Power gain vs. frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Figure 10. Input return loss vs. frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Figure 11. Drain efficiency vs. frequency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Figure 12. Drain efficiency vs. frequency at different drain voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Figure 13. Power out vs. drain voltage at different frequencies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Figure 14. Impedance data schematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Figure 15. PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 16. PD54008L-E amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

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Basic wireless meter reading system description	AN2048

1 Basic wireless meter reading system description

To reduce cost and difficulties associated with the reading of indoor utility meters for gas, water and electricity, a new automatic meter reading system has recently been introduced. It uses radio frequency networks and allows direct data communication between reading meters and services and/or the billing department. A DTU (Data Transmission Unit) module that contains a powerful UHF narrow-band radio transmitter is attached to gas, water and electric utility meters.

Figure 3. Network system

A DCU (Data Collector Unit) is placed in a convenient location within an apartment building or housing complex.

The DCU contacts daily an NCC (Network Control Computer) and forwards the meter reading information.

The NCC processes the information and provides billing data and customer support information. This paper describes a DTU solution using an STMicroelectronics 8 W - 7 V LDMOS device housed in a PowerFLAT and called PD54008L-E.

2Electrical requirements

●VDD=5 V IDQ = 10 mA frequency band [450 470] MHz

●Pout = 36 dBm gain flatness < 1dB

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